Nozzle shut-off device

ABSTRACT

In an injection molding apparatus, wherein a plasticizing chamber has a nozzle attached to one end thereof, with the nozzle having a passageway therein and being in communication with the sprue of a mold, the improvement which constitutes a compact, pneumatically-powered, reciprocable spool-type device having a passageway therein, operated by alternately actuated opposed pistons, interposed between the nozzle and the plasticizing chamber, in one position blocking the communication between the plasticizing chamber and the nozzle and in the other position allowing molten material to enter the nozzle.

BACKGROUND OF THE INVENTION

This invention relates to injection molding machines in general, butparticularly to the reciprocating screw or plunger type machine suitablefor the injection molding of plastic and elastomeric materials.Conventional molding apparatus of the reciprocating-rotating screw typeusually includes a plasticizing cylinder or chamber having a bore,wherein the plasticizing screw rotates in such a manner so as to allowthe solid molding material to enter the cylinder and be plasticized asit advances in the direction of screw feed. Attached on one end of theplasticizing cylinder is a nozzle in communication with a mold sprue. Asthe plasticized material is deposited at the metering or front end ofthe screw, it developes a back pressure that forces the screw to retractin the cylinder bore and when the plasticized material reaches apredetermined volume, or shot size, the retracting screw contacts alimit switch and stops its rotation. At this stage, the shot is readyfor injection into the mold, generally upon receipt of a signal from theclamp, whereupon the screw is driven forward hydraulically to inject theshot. Upon receipt of another signal, the plasticizing screw againstarts to rotate and gradually retract as a fresh shot is built up inthe plasticizing cylinder. Thus, the screw reciprocates once per machinecycle to plasticize and inject a shot of material.

Often, shut-off valves or devices are employed to interrupt the flow ofmolten material from the nozzle into the mold sprue. These offer theadvantages of minimizing or entirely curtailing drool through cut off ofmaterial flow at the nozzle and provide the capability to plasticizeduring periods in which the clamp is open. Generally, plasticizing takesplace during part curing to prevent plasticized material from escaping.

Over the years many types of shut-off devices and means to actuate themhave been developed and utilized with varying degrees of success.Included among these are, for example, spring operated needle valvessuch as shown in FIG. 4 of U.S. Patent 3,002,229, which are generallynot completely reliable in actual operation; mechanically operated pinvalves such as shown in U.S. Patent 3,172,161 which are generallydifficult to properly align and have multiple pivot points subject towear; hydraulically operated rotary valves such as shown in FIG. 3 ofU.S. Patent 3,169,275 which are often subject to scoring and difficultto locate near the nozzle because of high nozzle temperatures which makehydraulic operation hazardous; .[.and.]. hydraulically operated pistonvalves such as shown in FIG. 3 of U.S. Patent 3,026,567 which again aredifficult to locate near the nozzle due to the high nozzle temperaturesinvolved.[...]..Iadd.; and a pneumatic piston operated valve with afloating seal on a reciprocable valve gate member is described in U.S.Patent 2,936,996. .Iaddend.

SUMMARY OF THE INVENTION

This invention solves the previously mentioned problems by interposing acompact, pneumatically powered, reciprocable spool-type valve, operatedby alternately actuated opposed pistons, interposed between the nozzleand the plasticizing chamber. This nozzle shut-off valve is so compactas to be substantially contained wholly within a recess in the platenand is thusly located very close to the nozzle. Furthermore, it ispneumatically operated, i.e., by a source of pressure readily available,inexpensive, and presenting no fire hazard. This shut-off device mayalso be operated in any position, i.e., horizontally, vertically, ortherebetween and has a very minimum of moving parts. In addition, a verysimple piston-stroke adjusting means may be incorporated which allowsprecise spool alignment.

In summary, this invention provides a nozzle shut-off device which isinterposed between a nozzle having a passageway, and a plasticizingchamber, comprising a body having a first passageway in communicationwith both the plasticizing chamber and the nozzle passageway, a secondpassageway intersecting the first passageway, a spool reciprocable inand extending through the second passageway, and having a thirdpassageway capable of communication with the body first passageway,pistons attached to the ends of the spool, cylinders attached to thebody and encompassing the pistons, a source of fluid pressure and ameans to connect the source of fluid pressure alternately to thecylinders to pressurize one and vent the other, thus in one positionblocking the body first passageway and in the other position connectingthe spool third passageway with the body first passageway to allowmolten material to enter the nozzle.

Other features and advantages to the present invention should be readilyapparent by reference to the following specification, considered inconjunction with the accompanying drawings, and it is to be understoodthat any modification may be made in the exact structual detailsthereshown and described, within the scope of the appended claims,without departing from or exceeding the spirit of the invention.

DRAWING DESCRIPTION

FIG. 1 is an end view of the nozzle shut-off device interposed betweenthe nozzle and the plasticizing cylinder.

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1 and shows thenozzle shut-off device interposed between the nozzle and theplasticizing cylinder.

FIG. 3 is a sectional view taken along line 3--3 of FIG. 1 and shows theinstallation of an internal heating element.

FIG. 4 is a fragmentary view looking in the direction of arrow 4 in FIG.1.

DETAILED DESCRIPTION

Referring now to the drawings in detail, FIGS. 1 and 2 are an end viewand sectional view respectively of nozzle shut-off valve 50 interposedbetween nozzle 34 and plasticizing cylinder 10 of an injection moldingmachine having for example, chamber or hollow plasticizing cylinder 10composed of barrel 11, liner 12, and reciprocable and rotatableplasticizing screw 14 having screw tip 16 attached thereto, andflow-back valve 17 interposed therebetween. Cylinder end cap 18, havingcentral axial passageway 21, flat front face 19 and front facecylindrical recess 20, is mounted to one end of plasticizing cylinder 10by a series of equally spaced bolts 13. Heating elements, such asdenoted by numeral 15, may, for example, circumferentially surround endcap 18, nozzle 34, and all or part of barrel 11.

Nozzle 34, having central axial nozzle passageway 40, hemisphericalfront end surface 36, threaded portion 38 and concentric cylindricalrear end portion 39, has threaded portion 38 in such engagement withthreaded bore portion 42 of adaptor 44, also having four equally spacedcounter bored holes 46 and rear face 45, so that concentric cylindricalrear end portion 39 extends axially from adaptor 44 parallel to face 45.

Hemispherical front end surface 36 of nozzle 34 engages hemisphericalrecess 32 in mold 28 so as to allow communication, axial alignment to bespecific, between nozzle passageway 40 and sprue 30 of mold 28, with thelatter being aligned by locating ring 26 mounted on the inner end ofconical recess 24 in platen 22.

FIG. 2 shows concentric cylindrical end extension 39 of nozzle 34,extending from adaptor 44, into sealing contact with cylindrical recess64 in front face 62 of shut-off valve body 51, the latter to be fullydescribed later. Rear face 45 of adaptor 44 abuts front face 62 of valvebody 51, while concentric cylindrical rear face extension 68 of valvebody rear face 66 is in sealing contact with front face cylindricalrecess 20 of cylinder end cap 18. Cylindrical recesses 20 and 64 as wellas concentric cylindrical rear face extensions 39 and 68 aresubstantially similar in size and shape. Thus, it may be seen thatnozzle shut-off valve 50, interposed between nozzle 34 and plasticizingcylinder 10, is readily removable and that adaptor 44 may be directlyconnected to cylinder end cap 18 upon movement to the left byplasticizing cylinder 19, so that adaptor rear face 45 abuts end capflat front face 19 and that nozzle concentric cylindrical rear endextension 39 extends into sealing contact with front face cylindricalrecess 20. Direct connection, in the absence of nozzle shut-off valve50, between nozzle 34 and plasticizing cylinder 10 allows communication,axial alignment to be specific, between sprue 30, nozzle passageway 21in cylinder end cap 18.

Nozzle shut off device or valve means 50 is basically composed of valvebody 51, valve spool 80, pistons 90, 98, and cylinders 102, 122, all ofwhich will now be described in detail. Valve body 51, generallyrectangular in shape, has flat front face 62 with central cylindricalrecess 64 parallel with flat rear face 66 having central concentriccylindrical rear face extension 68, with central first axial passageway52 extending through valve body 51 and terminating at front and rearfaces 62, 66, respectively. As previously discussed, nozzle rear endextension 39 is in sealing contact with valve body front face recess 64,while valve body rear face extension 68 is in sealing contact withcylinder end cap front face cylindrical recess 20, thus allowingcommunication, axial alignment to be specific, between sprue 30, nozzlepassageway 40, valve body first passageway 52 and cylinder end cappassageway 21. In addition to first passageway 52, four equally spacedholes 56, axially aligned with holes 46 in adaptor 44, also extendbetween front and rear faces 62, 66, respectively and house bolts 60which concurrently attach adaptor 44 and valve body 51 to each other andto cylinder end cap 18. Valve body 51 further has flat opposed sidefaces 76 (FIGS. 1 and 4) and flat opposed side faces 70 havingcylindrical flat recesses 72, with the latter being the terminatingfaces of central second axial passageway 54 extending through valve body51, with second passageway 54 intersecting and being substantiallyperpendicular to first passageway 52.

Reciprocable in and extending from each end of second axial passageway54 is valve spool 80 composed of center portion 82, having thirdpassageway 86 parallel to and capable of axial alignment with firstaxial passageway 52 in valve body 51, and substantially similar firstand second end portions 83, 84, respectively. Attached in an axialdirection to valve spool first end portion 83 by means of two bolts 95is stepped cylindrical piston 90 having top surfaces 91, piston ring 92and partial bore 94 with one end of guide pin 96 being secured therein.Attached in an axial direction to valve spool second end portion 84 bymeans of two bolts 95 is stepped cylindrical piston 98, which issubstantially similar to piston 90, lacking only partial bore 94. Thetwo bolts 95 securing each piston 90 and 98 to valve spool 80 also serveto keep valve spool 80 from rotating with respect to pistons 90 and 98.

Peripherally encompassing piston 90 and attached to valve body 51 bymeans of multiples of bolts 142, 144, is cylinder 102 having side wall103, closed end 110, and open end 104, having recessed portion 106adjacent to valve body side face 70, with portion 106 being aligned withvalve body side face recess 72, thereby defining open-ended cavity 108,as best shown in FIG. 4. Cylinder closed end 110 has outer taperedportion 112, inner end surface 115 with recessed circular portion 116,partial bore 118 and partially threaded bore 120. Piston 90, fittingclosely within cavity 114, is able to reciprocate therein, with pistontop surface 91 being generally parallel with cylinder inner end surface115 and recessed portion 116. The other end of guide pin 96, secured topiston 90, is slidingly received in partial bore 118 thereby keepingpiston 90 from rotating with respect to cylinder 102.

Similar to the above description and using like numerals where possible,peripherally encompassing the piston 98 and attached to valve body 51 bymultiples of bolts 142, 144, is cylinder 122 having side wall 103,closed end 124, open end 104 having recessed portion 106 adjacent tovalve body side face 70, with portion 106 being aligned with valve bodyside face recess 72 to again define open-ended cavity 108. Cylinderclosed end 124 has outer tapered portion 130 with recess 132, inner endsurface 125 with recessed circular portion 116, partially threadedstepped bore 128 perpendicular to surface 125 and partially threadedbore 120. Piston 98 fitting closely within cavity 114 is able toreciprocate therein with piston top surface 99 being generally parallelwith cylinder inner end surfaces 125 and recessed portion 116.

Located in partially threaded stepped bore 128 is bolt or socket headcap screw 134, having its threaded portion including slot 136 extendingthrough cylinder closed end 124 into outer recess 132 wherein nut 140 isthreaded thereon and abuts cylinder 122. Top surface 135 of cap screw134 is generally flush with cylinder inner end surface 125 but may beadvanced into cavity 114 after loosening nut 140 and turning cap screw134 after inserting, for example, a screw driver into slot 136. Thus,cap screw 134 and nut 140 serve as a stroke adjusting means which limitsthe outward movement of piston 98, which is of importance since itcontrols the degree of axial alignment of valve body first passageway 52and valve spool third passageway 86. Based on manufacturing tolerances,assembly tolerances and cost, it is less practical to build a nozzleshut-off valve that provides precise axial alignment between passageways52 and 86 when this alignment can readily be accomplished at initialassembly by mere adjustment of cap screw 134 and nut 140. However,stroke adjusting means 134, 140, may be deleted if the tolerances areselected to provide satisfactory axial alignment between passageways 52and 86. As best seen in FIGS. 1 and 3, internal heating elements 55 maybe inserted into aligned holes 48 and 58 in nozzle adaptor 44 and valvebody 51, respectively. This construction is not mandatory however, sincean external band heater (not shown), similar to those denoted bynumerals 15, may readily be utilized on the peripheral surface ofadaptor 44.

In operation, a source of fluid under pressure, preferably air, isconnected generally by means of flexible hosing (not shown) to partiallythreaded bores 120 in cylinders 102 and 122. A switching means (notshown) is utilized to alternately pressurize one and vent the other ofcylinders 102, 122, thereby causing pistons 90, 98, and valve spool 80to reciprocate in unison, thus in one position, (when cylinder 122 ispressurized and cylinder 102 is vented) blocking first passageway 52 invalve body 51, and in the other position, as shown in FIG. 2 (whencylinder 102 is pressurized and cylinder 122 is vented) axially aligningthird passageway 86 in valve spool 80 with first passageway 52 in valvebody 51, thereupon allowing molten, generally plastic material, asdelivered by rotating and reciprocating screw 14 in plasticizingcylinder 10, to flow into cylinder end cap passageway 21, cylinder firstpassageway 52, valve spool third passageway 86 and nozzle passageway 40into sprue 30. If nozzle shut-off is desired, cylinder 102 is vented andcylinder 122 is pressurized, thereby shifting valve spool thirdpassageway 86 out of alignment or communication with valve body firstpassageway 52 thereby blocking the flow of molten material into nozzlepassageway 40. Although nozzle shut-off valve 50 may be operated in anyposition, i.e., horizontally, vertically, or therebetween, operationthat allows horizontal reciprocation of valve spool 80 is preferred.

Valve spool 80 and valve body second passageway 54 are substantiallycircular in cross-section, with valve spool central portion 82 beingsubstantially similar in diameter to that of second passageway 54 toinsure a close tolerance but smooth sliding fit. It must however benoted that valve spool 80 and valve body second passageway 54 are by nomeans restricted to being only circular in cross-section but may well benon-circular, rectangular, or even generally square, and in order tosimplify valve body construction for the latter two configurations,valve body 51 can be made of two parts, with the first part having asquare or rectangular recess into which modified spool 80 wouldreciprocably fit, with the second part being plate-like and serving acover function. Non-circular valve spool configuration also eliminatesthe need for multiples of bolts 95 and guide pin 96 since a non-circularvalve spool configuration will not allow valve spool 80 to rotate invalve body second passageway 54 and thus eliminates all axialmisalignment between valve spool third passageway 86 and valve bodyfirst passageway 52 possibly caused by valve spool rotation.

Valve body second passageway 54 and valve spool center portion 82 arecarefully lapped to obtain a smooth sliding fit of the latter in theformer to insure not only smooth, even, reciprocating movement,requiring a minimum of air pressure and giving clean, quick and completeshifts from open to closed position and vice versa, but to alsoabsolutely minimize the leakage of molten material from valve body firstpassageway 52 and valve spool third passageway 86 when valve spool 80 isshifted to closed position. It must be remembered that when valve spool80 is shifted to closed position, valve spool third passageway 86 willcontain a slug of molten material which, if tolerances are not keptclose, will tend to leak into passageway 54. Leakage between passageway54 and valve spool central portion 82 will not only increase the amountof pneumatic pressure required to shift valve spool 80 but can alsocause material and color contamination if these are changed. Inaddition, thermally sensitive materials may also tend to decompose andcould cause scoring.

This invention, as discussed above, minimizes molten material leakageand scoring but if some slight leakage should occur, substantiallysimilar valve spool end portions 83, 84, being somewhat smaller indiameter than valve spool central portion 82, will allow this moltenmaterial, due to the reciprocating spool movement, to flow axiallyoutwardly and away from valve spool central portion 82 into the spacebetween valve spool end portions 83, 84, and second passageway 54 fromwhere it will enter open ended cavities 108 defined by side facerecesses 72 and cylinder open end recessed portions 106. Allowingremoval of this leakage will reduce scoring.

Molten material entering open ended cavities 108, best shown in FIG. 4,will harmlessly drop out of open ended cavities 108 when nozzle shut offvalve 50 is oriented to allow horizontal reciprocation of valve spool80, during horizontal material injection, which orientation is preferredfor that .[.retson.]. .Iadd.reason.Iaddend.. However, even in otheroperating position all leakage is readily removable from cavities 108.In addition, open ended cavities 108 allow visual inspection of valvespool end portions 83, 84 not only for possible molten material leakagebut also to determine whether or not valve spool 80 is properly shiftingto and from its respective open and closed positions. Another benefit ofthis construction is that it reduces to a minimum the amount of heattransfer from valve body 51 to cylinders 102, 122, thereby minimizingcylinder and piston distortions.

An examination of FIG. 2 will show that nozzle shut-off valve 50 is socompact as to be substantially contained wholly within recess 24 ofplaten 22 and is thus located very close to nozzle 34. In addition,penumatic operation is desirable since it presents no difficult orexpensive sealing problems as is the case with hydraulic operation, andcompressed air is generally readily available, inexpensive, and presentsno fire hazards.

While this invention has been described in connection with possibleforms or embodiments thereof, it is to be understood that the presentdisclosure is illustrative rather than restrictive and that changes ormodifications may be resorted to without departing from the spirit ofinvention or scope of the claims which follow.

What is claimed is: .[.
 1. In an injection molding apparatus comprisinga chamber having a nozzle attached near one end thereof, means forforcing molten material from said chamber through a passageway formed insaid nozzle, a mold having a sprue formed therein, which sprue is incommunication with the passageway formed in said nozzle, and a nozzleshut-off device interposed between said nozzle and said chamber theimprovement comprising:(a) a body for said device having a firstpassageway in communication with both said chamber and the passagewayformed in said nozzle and a second passageway intersecting said firstpassageway; (b) a spool reciprocal in the second passageway of said bodyand having a third passageway capable of communicating with the firstpassageway of said body; (c) a piston attached to each end of saidspool; (d) a cylinder encompassing each of said pistons, said cylinderseach having a closed end and an open end, with said open end beingadjacent to said body and said cylinders being attached to said body;(e) a source of fluid pressure; and (f) means to connect said source offluid pressure alternately to said cylinders to pressurize one and ventthe other of said cylinders, thus causing said spool to reciprocate,thereby in one position blocking the first passageway in said body andin the other position connecting the third passageway in said spool withthe first passageway in said body, thus allowing molten material to passfrom said chamber into said nozzle..]. .[.2. In an injection moldingapparatus comprising a plasticizing cylinder having a nozzle attachednear one end thereof, means for forcing molten material from saidcylinder through a passageway formed in said nozzle, a mold having asprue formed therein, which sprue is in communication with saidpassageway formed in said nozzle, and valve means interposed betweensaid nozzle and said cylinder the improvement comprising: (a) a valvebody having a first passageway in communication with said cylinder andin axial alignment with the passageway formed in said nozzle and asecond passageway intersecting said first passageway; (b) a valve spoolreciprocable in the second passageway of said valve body and having athird passageway capable of axial alignment with the first passageway ofsaid valve body; (c) a piston attached to each end of said valve spool;(d) a cylinder encompassing each of said pistons, said cylinders eachhaving one closed end and one open end, with said open end being ajacentto said valve body and said cylinders each being attached to said valvebody; (e) a source of fluid under pressure; and (f) means to connectsaid source of fluid under pressure alternately to said cylinders topressurize one and vent the other of said cylinders, thereby causingsaid pistons and valve spool to reciprocate, thus in one positionblocking the first passageway in said valve body and in the otherposition axially aligning the third passageway in said valvespool withthe first passageway in said valve body, thereupon allowing moltenmaterial to enter said nozzle from said plasticizing cylinder..]. .[.3.In an injection molding apparatus comprising a temperature controllablecylinder having a nozzle attached to one end thereof, means for forcingmolten material from said cylinder through a passageway formed in saidnozzle, a platen with a mold having a sprue formed therein, which sprueis in communication with said passageway formed in said nozzle, and anozzle shut-off valve interposed between said nozzle and said chamber,the improvement comprising: (a) a valve body having a first passagewayin axial alignment with both said cylinder and the passageway formed insaid nozzle and a second passageway intersecting said first passageway;(b) a valve spool reciprocable in the second passageway of said valvebody and having a third passageway parallel to and capable of axialalignment with the first passageway of said valve body; (c) a pistonattached in an axial direction to each end of said valve spool; (d) acylinder peripherally encompassing each of said pistons and having oneclosed end and one open end with said open end being adjacent to saidvalve body and said cylinders each being attached to said valve body;(e) a source of fluid under pressure; and (f) means to connect saidsource of fluid under pressure alternately to said cylinders, topressurize one and vent the other of said cylinders, thereby causingsaid pistons and valve spool to reciprocate in unison, thus in oneposition blocking the first passageway in said valve body and in theother position axially aligning the third passageway in said valve spoolwith the first passageway in said valve body, thereupon allowing moltenmaterial to enter said nozzle from said temperature controllablecylinder..].
 4. The injection molding apparatus of claim .[.3.]..Iadd.11 .Iaddend.wherein the second passageway in said valve body issubstantially perpendicular to the first passageway in said valve body.5. The injection molding apparatus of claim .[.3.]. .Iadd.11.Iaddend.wherein the second passageway of said valve body and said valvespool are substantially circular in cross-section and of substantiallyequal diameters. .[.6. The injection molding apparatus of claim 3 withthe addition of a piston-stroke adjusting means incorporated in at leastone of said cylinders..].
 7. The injection molding apparatus of claim 11wherein the piston-stroke adjusting means comprises a nut and boltassembly incorporated in the closed end of at least one of saidcylinders.
 8. The injection molding apparatus of claim .[.3.]. .Iadd.11.Iaddend.wherein the fluid under pressure which causes said pistons andvalve spool to reciprocate is air. .[.9. The injection molding apparatusof claim 3 wherein said nozzle shut-off valve in addition to beinginterposed between said nozzle and said cylinder is also substantiallycontained within a recess in said platen..].
 10. The injection moldingapparatus of claim .[.3.]. .Iadd.11 .Iaddend.with the addition of atleast one internal heating element incorporated into said valve body..Iadd.11. In an injection molding apparatus comprising a temperaturecontrollable cylinder having a nozzle attached to one end thereof, meansfor forcing molten material from said cylinder through a passagewayformed in said nozzle, a platen with a mold having a sprue formedtherein, which sprue is in communication with said passageway formed insaid nozzle, and a nozzle shut-off valve interposed between said nozzleand said cylinder, the improvement comprising:(a) a valve body having afirst passageway in axial alignment with both said cylinder and thepassageway formed in said nozzle and a second passageway intersectingsaid first passageway; (b) a valve spool reciprocable in the secondpassageway of said valve body and having a third passageway parallel toand capable of axial alignment with the first passageway of said valvebody; (c) a piston attached in an axial direction to each end of saidvalve spool; (d) a cylinder peripherally encompassing each of saidpistons and having one closed end and one open end with said open endbeing adjacent to said valve body and said cylinders each being attachedto said valve body; (e) a piston-stroke adjusting means incorporated inat least one of said cylinders; (f) a source of fluid under pressure;and (g) means to connect said source of fluid under pressure alternatelyto said cylinders, to pressurize one and vent the other of saidcylinders, thereby causing said pistons and valve spool to reciprocatein unison, thus in one position blocking the first passageway in saidvalve body and in the other position axially aligning the thirdpassageway in said valve spool with the first passageway in said valvebody, thereupon allowing molten material to enter said nozzle from saidtemperature controllable cylinder. .Iaddend. .Iadd.12. In an injectionmolding apparatus comprising a temperature controllable cylinder havinga nozzle attached to one end thereof, means for forcing molten materialfrom said cylinder through a passageway formed in said nozzle, a platenwith a mold having a sprue formed therein, which sprue is incommunication with said passageway formed in said nozzle, and a nozzleshut-off valve interposed between said nozzle and said cylinder, theimprovement comprising:(a) a valve body having a first passageway inaxial alignment with both said cylinder and the passageway formed insaid nozzle and a second passageway intersecting said first passageway;(b) a valve spool reciprocable in the second passageway of said valvebody and having a third passageway parallel to and capable of axialalignment with the first passageway of said valve body; (c) a pistonattached in an axial direction to each end of said valve spool; (d) acylinder peripherally encompassing each of said pistons and having oneclosed end and one open end with said open end being adjacent to saidvalve body and said cylinders each being attached to said valve body;(e) said platen having a recess therein located and sized tosubstantially contain said nozzle shut-off valve; (f) said nozzleshut-off valve being disposed substantially within said recess; (g) asource of fluid under pressure; and (h) means to connect said source offluid under pressure alternately to said cylinders, to pressurize oneand vent the other of said cylinders, thereby causing said pistons andvalve spool to reciprocate in unison, thus in one position blocking thefirst passageway in said valve body and in the other position axiallyaligning the third passageway in said valve spool with the firstpassageway in said valve body, thereupon allowing molten material toenter said nozzle from said temperature controllable cylinder. .Iaddend.